IEEE 802.16 was established as a standard for radio MAN (Metropolitan Area Network), initially for FWA (Fixed Wireless Access) use, and it originally supports techniques for realizing high-efficiency radio transmission through high-level optimization of base stations, such as QoS (Quality of Service), AAS (Adaptive Antenna System), transmission diversity, etc.
Recently, schemes with excellent frequency-selective fading tolerance have been added thereto, such as OFDM (Orthogonal Frequency Division Multiplexing) and OFDMA (Orthogonal Frequency Division Multiple Access), and it now deals with radio access communications in multipath environments unanticipatedly.
With this situation, in mobile communications, expansions are now in progress mainly with OFDMA that offers subchannelization of individual terminal stations and is capable of handling propagation environments varying independently among the terminal stations.
Now, a conventional OFDMA technique will be described.
FIGS. 13 to 15 show a technique described in the IEEE 802.16 (IEEE P802.16-REVd/D5-2004, downloaded on 2004.11.8), for example, where FIG. 13 illustrates a sector configuration in which one cell is divided into three sectors, FIG. 14 illustrates the configuration of a radio base-station apparatus divided into segments corresponding to individual sectors, and FIG. 15 illustrates the OFDMA frame structure.
In FIG. 13, a cell 100 is divided into three sectors 101a, 101b and 101c. The cell 100 has a radio base-station apparatus 103 having antennas 102a, 102b and 102c for sending and receiving radio signals to and from terminal stations (not shown) located in the areas of the sectors 101a, 101b and 101c. 
In FIG. 14, the radio base-station apparatus 103 includes PHY (physical layer) processing blocks 104a, 104b and 104c for performing OFDMA modulation/demodulation and frame formation respectively for the sectors 101a, 101b and 101c, radio transmitter/receiver blocks 105a, 105b and 105c for sending and receiving radio signals through the antennas 102a, 102b and 102c to and from terminal stations not shown, a MAC (Media Access Control) processing block 106 for performing data allocation to the individual segments corresponding to the sectors 101a, 101b and 101c, and a network I/F 107 connected to the MAC processing block 106 through a network or the like not shown.
In FIG. 15, the vertical axis shows the entire band of radio frequencies used with logical subchannel numbers 110, and the horizontal axis shows time with OFDMA symbol numbers 111. The logical subchannel numbers 110 are divided into three segments in correspondence with the sectors 101a, 101b and 101c. The logical subchannel numbers 110 and OFDMA symbol numbers 111 thus form frames 112a, 112b and 112c for individual sectors 101a, 101b and 101c, which respectively include, sequentially from the beginning, preambles 113a, 113b and 113c, broadcast information 114a, 114b and 114c, downlink allocation information 115a, 115b and 115c, uplink allocation information 116a, 116b and 116c, downlink data regions 117a, 117b and 117c, and uplink data regions 118a, 118b and 118c. The broadcast information 114a, 114b and 114c, downlink allocation information 115a, 115b and 115c, and uplink allocation information 116a, 116b and 116c form frame control information.
Next, its operation will be described referring to FIGS. 13 to 15.
The MAC processing block 106 performs segmentation processing by dividing the entire radio frequency band for the logical subchannel numbers 110 into three segments corresponding to the sectors 101a, 101b and 101c, and allocating data to the individual segments.
Next, with the three segments corresponding to the sectors 101a, 101b and 101c, the PHY processing blocks 104a, 104b and 104c respectively generate the frames 112a, 112b and 112c and perform OFDMA modulation/demodulation processing, with the frames 112a, 112b and 112c respectively including, sequentially from the beginning, the preambles 113a, 113b and 113c, the broadcast information 114a, 114b and 114c, the downlink allocation information 115a, 115b and 115c, the uplink allocation information 116a, 116b and 116c, the downlink data regions 117a, 117b and 117c, and the uplink data regions 118a, 118b and 118c. 
Then, the radio transmitter/receiver blocks 105a, 105b and 105c perform frequency conversion and amplification processing to enable radio-signal transmission/reception with terminal stations, and radio signals are transmitted to and received from terminal stations through the antennas 102a, 102b and 102c. 
Non-Patent Document 1: IEEE P802.16-REVd/D5-2004, downloaded on 2004.11.8.